This invention relates to cardiac leads used in combination with a cardiac rhythm management device, e.g., heart pacemaker or defibrillator, to monitor and control the rhythm of the heart. This invention is more particularly directed toward transvenous lead configurations adapted to be implanted in the coronary sinus (CS) or a coronary vein and to methods for implanting such leads.
Transvenous lead placement into the CS or deeper into the great cardiac vein or other coronary vein has recently become an important technique for cardiac pacing and defibrillation electrode implantation. For example, pacing the left ventricle (LV) from within a coronary vein appears to improve hemodynamics in certain heart failure patients. As another example, biatrial pacing, with the left atrium paced from the CS, is being studied to reduce the incidence of paroxysms of atrial fibrillation. As yet another example, defibrillation electrodes within the CS have been shown to reduce atrial and ventricular defibrillation thresholds.
U.S. Pat. No. 4,932,407 to Williams; U.S. Pat. No. 5,099,838 to Bardy; and U.S. Pat. Nos. 5,348,021; 5,433,729; and 5,350,404 to Adams et al., incorporated herein by reference, describe inserting a lead through the right atrium (RA) and CS into one of the coronary veins. None of these patents, however, discuss the difficulties encountered in doing so.
Fast and accurate placement of temporary or permanent leads into specific cardiovascular locations is difficult at best. For example, when the target location is the CS for left-sided pacing or defibrillation, the lead must follow a restrictive, tortuous path, and guidewire systems for leads are not yet capable of providing perfect control for simple placement. Current techniques practiced by implanting physicians usually involve guiding the lead to the desired location using tactile senses with fluoroscopic assistance.
These methods do not provide adequate feedback for consistently successful results. Furthermore, a semicircular valve, called the valve of Thebesius, protects the opening of the CS (the CS os), making it a difficult target. There is typically a learning curve associated with these procedures and thus there is a need for improved devices and methods for implanting leads. Furthermore, the profile of the distal end of a lead implanted in a coronary vein should be made as small as possible to limit occlusion of flow through the blood vessel when the lead is in place and to limit damage to the vessels. This requirement precludes the use of elaborate placement devices that add bulk to the lead.
U.S. Pat. No. 5,755,766 to Chastain et al. uses an existing lumen that houses a conductor for introducing a contrast agent as an aid in implanting the lead. One drawback to this arrangement is that if the existing conductor lumen is open from the connector to the patient""s body, contrast agent (if not flushed), saline (from flushing), or blood (over the long term) may be allowed to enter into the header. This may lead to electrical shorting between connector blocks should sealing rings lose their seal or the encapsulation header material delaminate from the connector blocks and allow a fluid path between connections. In one embodiment of Chastain et al., a plug is deployed to close the distal opening and seal the lumen; this may prove difficult when working from the proximal end of the lead through a small lumen. Furthermore, the structure of Chastain et al. limits delivery of the contrast agent to be from the distal tip of the lead. The present invention is not so limiting and permits the agent to be advantageously delivered radially from the side wall of the distal end of the lead.
It is therefore the object of this invention to provide both a device and a procedure that facilitate quicker, simpler, and more accurate lead placement into the desired final location, such as the CS or other cardiovascular structures.
The present invention provides an improved lead for implantation of an electrode into a coronary vein on the left side of the heart. The lead includes an elongated, flexible body member made of an electrically insulative material. The body member includes a proximal end and a distal end. A lumen extends through the body member from the proximal end toward the distal end. The lumen may extend all the way to the distal end so that the distal end includes an opening. The lead also includes a conductive member positioned alongside the lumen and extending through the body member from the proximal end toward the distal end. Electrically coupled to the conductive member near its distal end is an electrode. Additional lumens, electrodes and conductive members may be included within and on the lead body.
The cardiac lead of this invention has a lumen through which a radiopaque fluid may be injected. This lumen may be significantly smaller in diameter than other lumens used to house electrical conductors or accept stylets or guidewires, which are typically at least 0.014 inches in diameter. A radiopaque fluid is injected through the proximal end of the lumen and dispensed from a distal location, preferably as close to the distal tip as possible. A 0.003-inch diameter lumen would allow the passage of an appropriate commercially available radiopaque fluid. Thus, the overall diameter of the lead would not be significantly increased over a lead without such a lumen.
To implant a lead made in conformance with the present invention, the implanter passes the lead through a guide catheter, or introducer, until it is in or near the CS. This is done using a standard technique of stiffening the lead with a stylet, guiding the stiffened lead by hand through the RA and into or near the CS, aided by fluoroscopy. When the implanter wants to visually confirm that the lead is in the CS, he delivers a bolus of contrast agent through the small lumen and out the distal end of the lead. If the lead is in the CS, the bolus will be observed under fluoroscopy to travel back along the length of the lead, since the blood flow in the CS is returning to the RA and the lead will appear to be heading xe2x80x9cupstreamxe2x80x9d. If the lead is not in the CS but is still in the RA, the bolus will be seen squirting out from the tip in a forward manner before becoming diluted in the RA. Following proper placement, any stiffening stylets or guide catheters are retracted and the lumen may be flushed of all contrast agent with sterile saline.
The distal exit port may comprise a slit in the lead sidewall. This design prevents tissue ingrowth and maintains the patency of the lumen for possible future use.
The proximal end of the lead may incorporate a Luer lock that is detachable so it does not need to be implanted. The Luer lock may be connected to a short length of tubing having a lumen that forms a continuous channel with the lead body lumen for contrast delivery.